The present invention relates to linear displacement sensors and in particular to a Hall effect linear displacement sensor utilizing DC input power and providing a DC output. The sensor translates a variable linear core displacement to one or more DC outputs. Multiple output sensors find use as primary control elements in aircraft and other applications requiring one or more output signals. Heretofore the prevalent sensor for such applications consists of several linear variable differential transformers (LVDTs) assembled in parallel configuration.
Such a system is shown in U.S. Pat. No. 4,807,516 to Imre Takats. This patent discloses an aircraft flight control system employing three controllers operating as dual actuators. FIG. 1 of Takats depicts two dual LVDT assemblies which are AC devices requiring an AC power source for input power excitation and requiring a demodulator for output voltage measurement. Each of the LVDTs requires a separate core-rod assembly and parallel core-rod assemblies are attached to a yoke containing a ball bearing assembly for attachment to a single rod. Many aircraft control systems include dual triple or quadruple LVDT systems.
The prior art also includes a lateral displacement of a permanent magnet inducing a flux flow through a Hall effect device which in turn generates an output voltage indicative of the position of the permanent magnet with respect to the Hall effect device. Such arrangements are generally taught in U.S. Pat. Nos. 4,319,236; 4,107,604 and 4,322,709. The later reference relies on a magnetic circuit having a variable air gap with an increasing flux density used to activate a switch.
It is the object of the present invention to provide a displacement sensor which eliminates the need for the AC power supply, demodulator and elaborate mechanical rod assembly required of the prior art.
A farther object is to provide such a sensor which has a DC input and provides a DC output and one in which a single rod may be used to provide more than one output voltage.
A still further object is to provide a sensor that is not susceptible to external demagnetization of its magnetic element by utilizing a core made of a soft iron magnetic material rather than a permanent magnet.
Still another object is to provide a core position sensor whose output voltage magnitude and polarity may be adjusted over its displacement range by varying the coil excitation voltage, whose design is relatively simple, small in size and inexpensive to produce.
The above objects and advantages are attained in accordance with the present invention by providing a Hall effect magnetic core displacement sensor comprised of an electrical sensing assembly and a core rod assembly contained within a housing of magnetic material. The electrical sensing assembly consists of a bobbin of non-magnetic material about which a coil of electrically conductive, insulated wire is wound and a Hall effect device disposed about the coil. The Hall effect device is positioned about a line of symmetry of the bobbin/coil assembly. The core consists of a soft magnetic material in the form of a cylinder that is attached to a cylindrical rod made of a non-magnetic material.